Method for calcination



Aug. 4, 1953 P4B. KEMMER METHOD FOR CALCINATION Filed Oct. 12. 1950 NIH.,a NN n :lull/lll Patented Aug. 4, 1953 UNITED TATES 'PAT ENT `O FF ICEMETHOD FOR CALCINATION Frank R. Kommer, Larchmont, N Y.

Application ctoher 12, 1950, Serial Nol 189,749

1 Claim. l This invention relates to amethod land .apparatus for heattreating materials in rotary kilns.

The'invention is particularly useful' in vthe carl.- cining of Portland'cement @linker rand, for that reason', will vbe lirs't `illustrated bydescription in connection with such use.

IThe method and apparatus fof the invention make possible an increase ofa filfth or somewhat more in the capacity of the same kiln fired in aconventional manner and with a usual burner,

produce an abnormally high and desirable temperature in the -olinker atthe discharge end of 'the ki-ln`shorten the combustion zone, and thusdecrease the length of kiln required.

The invent-ion provides also a method and apparatus in which powderedanthracite coal may he used as the fuel, in those regio-ns in whichanthracite is mined locally and is the least eX- pensive fuel. Thecomplete substitution of anthracite for such usual fuels as oil, gas, orpfowdered bituminous coal has not been successful heretofore in cementmanufacture; the low content of volatile matter and the high`percentagvze of fixed carbon in anthracite coal retard the comi.

'bustion' of this coal when it is tried as the powdered uel in a cementkiln. As a result, the flame is not of the usual plume shape but isconsider- 'ahly longer. The long flame gives more Wide distribution ofthe heat and less concentration of it Where desired in the firing end ofthe kiln. The limit -tothe amount of anthracite that may be substitutedhas been around 50% of the total weight of coal used in the firingprocess.

Briefly stated, the invention comprises .a burner for anaerformsuspension of a fluid fuel or'powdered coal, the burner having a slitorifice servlng' to shape the llame of the burning fuelv into a natband, and means for approximately parallel- ,izing the band flame, bothangularly and longitudinally, with the surface of the charge in thekiln. In the preferred embodiment, the invention includes also means fordirecting a stream 'of secondary air, for the combustion or the fuel,between the lbandV llame and the cement or other material being heated?.This apparatus in operation gives a band llame in close proximity to theeinncsed surface of the charge and approximately parallel thereto.

The invention comprises, also., the `method of heat treating material'with the spaced band or ribbon flame as described herein..

The inventionk will be; further illustrated by description in connectionwith. the. attached drawings 'to which inference` is made.

Fig. l shows a side sectional view of the 'firing (Cl. 26S-52) 2 `end.of .a .rotary kiln constructed in accordance with the invention.

Fig. 2 is 4a ysectional View online A2.--2 of Fig. l.

Fig. 3 is a sectional view on line 3--3 of Fig. l.

Fig. 4 is a sectional view on line 4--4 of Fig. l.

Thesectional views are in the direction of the arrows on the respectivesection lines. The figures are .in part diagrammatic. The parts notillustrated are conventional.

There are shown :an inclined rotary kiln with outer lshell l0 driven lbyconventional ring `gear l2 and gear wheel l'd, the ycharge |-6`undergoing heat treatment, and' va layer I8 of the material of thecharge cakedupon the refractory lining 2,0 inside the shell of thekil-n. l

The burner 22 hasv a discharge end v24 in the lshapel of a slit. Theslit is vangular-ly inclined, asshown in Fig.l 2, so that the flame 26is approximately parallel to the exposed surface of the material I6'being 4heat treated. While the flame v26 spreads andbecomes irregular,it retains the general form of a ribbon or band.

Secondary .air is admitted through the duct 28 and drawn upward` yby thenatural draft of the system. A deecting baille 3S extends across. thewall 32 of the duct and dellects the stream of secondary air, to theIright in Fig. l, that iis, under and into the band flame 2B. Thisdirection of the secondary air prevents the band llame from strikingdown for any substantial period of time upon the material being heated.This direction of the secondary air also promotes prompt combustion ofthe fuel.

Another deflector 3l is mounted on the side wall of the hood or tiringhead. It may be a part of the ceramic or cement construction of the headas shown, for instance, in Fig. 2. The location of this second deflectoris adjacent to the end of the kiln and on the up-side thereof as thekiln is rotated. The position is. below the level of the upper edge ofthe band llame. This deector ex'- tends in a sloping manner generallytoward this upper edge of the flame. This delector 3| serves the purposeof tilting the stream of secondary air, so as to cause its upper surfaceto parallel more closelyv the angle of the band name.

In case of cement manufacture, secondary air ordinarily is that whichissues from the elink'- er cooler.4 disposed below the rotary kiln. In arepresentative run with the apparatus described, vthe temperaturey ofthe secondary air delivered from the cooler to the kiln. was 819 F., ascom.- pared.- to only 692 for the same setup with standard.. round.'burner andy plu-me flame.

Materials of construction for the various parte of: the kiln firing end:described are those which 'clination downward towards the down tothezone IB.

ffmerely 'lelizing This parallelizing of the burner and the are usual inapparatus of this kind. Thus, the shell I in the kiln may be steel, thelining 20 a high grade refractory block, the duct 28 l'lre brick, theburner 22 with the slit opening 24 steel, and the deflector 30 fire clayin fired condition.

Some of the principal advantages of the invention are stated above.There are others.

What is desired in the calcination of cement or the like is intense heattransfer by radiation. The equipment shown in Figs. 1 and 2, forinstance, keeps the flame out of contact with the said material andinthe quadrant or quarter of the kiln containing material I6. The flameis in extremely close juxtaposition to the material, however, so thatthe radiation to the material is much greater for unit area of exposedsurface thereof than to the more remote parts of the circumference ofthe kiln. There is obtained not only increased transfer of heat to thematerialto be calcined, with proportionate attendant in-I cr'easein therate at whichLthe material may be fed through the kiln, but alsoadecreasedper- -centage o'f'thetotal heat .lost .through the kiln As aresult of lesser heating. of the kiln lining, there is a decrease inthethickness of the caked layer I8 inside the kiln, as from the usual Sor 9inches to about to 6 inches. This increases the effective free spacewithin the kiln.

Using this system in Portland cement manufacture, there is possible anincrease of vproduc- 'tion per kiln in excess of 18% of the normal pro--duction' capacity.' To obtain this increase of capacity, withoutdecrease ofthe `final temperae ture of calcination below theu'sualVthespeed of rotation of the kiln'is increased. l

With the apparatus and method described, the firingzone in the cementkiln may be shortened from the usual 25-30 feet to 15-20 feet.

The operation of the equipment and the method will be evident from thediscussion that has been given above. In general, thekilnis mounted at aslight indischarge end andy 'rotated ina usual manner. The fuel if oilis atomized' or if coal is suspended in finely powdered form in thebarrel of the burner-22. The atomizing or suspending medium isair. Theatomized oil or the aeriform lsuspension of the coal is then deliveredthrough the slit 24 constituting the firing or discharge end of theburner. Natural gas may be used as the fuel, with all the air for itscombustion introduced outside the stream of the gas issuing from theslit inthe burner. 4 n

The burner is mounted by usual means, as by bolts securing it to asupporting framework (not shown) at such an angle radially that" thelength ofthe slit 24 is approximately parallel'to'the exposed surface ofthe material being calcined.

`This gives a flame that at the start is also approximately parallel -tothe s aidfsurface, all as shown in Figs. 2 and 4. In the case of cementclinker this angle of repose in the rotating kiln is about as shown inFig. 2. The :angle varies somewhat and reaches about the angle shown bythe steeper line Il. before-sliding or tumbling In addition to theangular mounting of the burner radially inthe manner stated, the`mounting meansA also establish the longitudinal axis of theburnerapproximately in the sameslope as the slope of the rotarykilnitself. The means are usual, the. setting being yadjusted to givethelongitudinal paral- .or powdered coal burner.

band shaped name issuing from the burner prevent the flame, as itextends into the kiln, from striking down on the material being calcinedand the stream of secondary air under the flame furnishes additionalprotection against overheating; the invention includes not only theparallelizing of the burner and the band flame with the kiln, as stated,but also the discovery that striking of the flame at a sharp angle uponthe material being calcined is objectionable and in fact is notpermissible, particularly when there is used a fuel of such greatcaloric power as powdered anthracite coal.

With the condition described, it is now possible to substitute powderedanthracite to the extent of 100% for bituminous coal or oil.

It isl possible under my conditions also to form quickly the coating I8in the firing end of the kiln. VThis quick formation of the coating iscontrary to experience with the conventional piume flame of acylindrical burner. v. With the conventional ,burner and llame, thereisconsiderable Vlapseof time after akiln has been rebrickedand placedunder Afire before the coating yI8 forms.

..cined. In general, the size ofthe slit is one which has approximatelythe same area as the conventional round outlet of the usual type of oilWe have found particularly satisfactory results when thelength of theburner slit is4 about tento ninety times the width of the slit. Withcoal, dimensions that .are suitable for the outlet slitin the burner arelengths ofl 3 to 6 feet and lwidths of to 2 inches or so. The length ofthe burner slit will be larger, the larger the kiln diameter. Three feetlis about the right length of slit for a 9 foot kiln and vefeet for a 12foot kiln. l

In general, the length of theslit in the burner is about 30% to 40% ofthe overall diameter of the kiln;-that is of the shell l0, or about v20%to 30% less than the width ofthe exposed surface ofthe charge beingcalcined and represented by I5 in the drawings. p

The spacing of the burner is about 4 to 10 inches above the level ofthe. upper surface of material I6. Y

The invention will` be further illustrated by the specific example ofthe practice of it.

Example I have applied my method and apparatus to a rotating kiln havinga steel shell 9 feet in diameter by 1,25 feet long, with a lining ofrefractory 6 inches thick, with aconventionalburner of a diameter of 8inches, Vand-with powdered bituminous coal asthe fuel. The ordinaryplumelike flame made possible an output of clinker averaging 39 barrelsper hour. With my slit burner, of length of slit approximately 3 feetand width'l, inch, I increasedtheoutput to an average of 46.2 barrels ofcement clinker pei` hour,

va gain of 18% in rate of production.

method, Thus the flame temperature was raised by approximately 43 F. to2746 F., with the possibility of maintaining a flame temperature of 3000F. if desired. IThe temperature of clinker discharge from the kiln was2l70 F. as compared to 2040" F. in the conventional operation. Thetemperature to which the secondary air was preheated in the clinkercooler was 760 F. as compared to 600 F. with the usual round burner. Ina series of separate kilns in which my method and apparatus were used,it was found in each instance that the speed of the kiln could beincreased. In fact, the speed was increased. Also the speed of theclinker cooler was increased, to take away the clinker and preventaccumulation of the increased production to an undesirable depth in thebed in the cooler. The proportion of total heat supplied which goes intothe nished product was increased, with resulting fuel economy per barrelof cement made.

The procedure of the example and the general method described is usefulalso in calcining limestone to lime, aluminum hydrate to alumina,magnesite to magnesa for basic refractories, sintering red mud frombauxite rening by the Bayer process, nodulizing ores of iron ormanganese, and volatilizing zinc oxide from zinc plant residues.

So used, my method and apparatus give increased capacity per` kiln andfuel economy per ton of output. Also there may be used anthracite to theextent of '75% or so, the remainder being oil or bituminous coal. Forsome uses, anthracite may be employed exclusively.

When the material is changed from the Portland cement of the example,the temperature established in the material is made that which isaccepted practice for the particular material used. The rate of feed andconsequently the rate of production per kiln is increased, however,

to make full use of the greater rate of heat trans'- fer from theclosely spaced wide band of llame to the material being processed.

It will be understood that it is intended to cover all changes andmodications of the examples of the invention herein chosen for thepurpose of illustration which do not constitute departure from thespirit and scope of the invention.

What is claimed is:

The method of heat treating material in an inclined rotary kiln whichcomprises advancing the material with inclined exposed surface throughthe kiln by rotation thereof, introducing into the lower quadrant of thefiring end of the kiln, which quadrant contains the material to betreated, a ame that extends generally parallel to the length of thekiln, that is of the general shape of a band, that is disposed in closeproximty to the inclined surface of the said material, and that istilted so that the flame is approximately parallel to the angle ofrepose of the said material, and introducing and deflecting a protectivestream of air between the said band and material, so that the stream isguided into a path that is approximately parallel to the flame andsurface of the said material, the introduction of the air serving toprevent contact of the name with the material.

FRANK R. KEMMER.

References Cited in the le of this patent UNITED STATES PATENTS NumberName Date 2,034,180 Glenn Mar. 17, 1936 2,487,369 Plotner Nov. 8, 19492,555,289 Nagel May 29, 1951 2,584,808 Newhouse Feb. 5, 1952

